A fiber ring network is a collection of nodes forming a closed loop, where each node is connected via a duplex communications facility. The multiplexing devices used in the SDH/SONET ring architecture are Add Drop Multiplexers (ADM) that add and drop local channels and pass through transit channels. A Self-Healing Ring is a ring network that provides redundant bandwidth so that disrupted services can automatically be restored following network failures.
Present technology, as disclosed in U.S. Pat. No. 5,185,736 to Tyrrel et al. can only provide protection against fiber failure, not node failure. In U.S. Pat. No. 4,704,713 to Haller et al. is shown a method for dealing with the node failure, but no fiber failure. Additionally, this solution is not transparent to services, bit rate and code format, due to the electro-optical conversion in every second node.
Wavelength Division Multiplexing has so far been focusing on packet switched networks as disclosed in U.S. Pat. No. 4,979,879 to Habbab et al.; U.S. Pat. No. 4,797,879 to Eda; U.S. Pat. No. 5,208,692 to McMahon. All of these solutions are for Local Area Networks (LAN), and are not competitors to SDH/SONET systems.
A SDH/SONET ring is costly to upgrade. If changes are made in one subnode, e.g., increasing the bit rate, changes have to be made in all the other subnodes around the ring as well. However, with the introduction of a multi-wavelength based network layer the flexibility can be extended even more. New transmission formats can be introduced on different wavelengths and in the same fiber network, e.g., a physical ring.
When the total traffic flow concentrates in the same fiber, the demand for protection of the ring increases. A desirable protection feature is a simple, fast and efficient handling whenever a fault occurs.